In a typical residential underground loop distribution circuit system, it is usually considered desirable to break the loop near the center of the load. This is normally effectuated by parking one of the primary cable elbows in a standoff insulator mounted in the parking stand. While it is recognized that there are severe problems of underground cable failure in such systems due to lightning and reflected wave damage to the parked cable, particularly at higher voltages, most utilities presently employ no protection whatsoever and instead place reliance on the arrester at the riser pole.
Notwithstanding the general absence of underground cable protection, there now appears to be a strong predisposition toward applying arrestors at the open end of the loop to prevent the voltage wave from doubling as it reflects off the end of the line. The most common form of underground cable protection in use today is an arrangement employing two elbow arresters in a pad mounted transformer at the open point in the distribution loop. In this arrangement, one elbow arrester is installed on the bushing of a transformer left vacated by the removal of one of the primary cable elbows. The other elbow arrester is typically installed on a portable feedthrough device mounted in the parking stand between the primary bushings. The cable removed from the transformer is also installed on the feedthrough device, whereby protection is furnished to the disconnected cable.